1. Field of the Invention
The disclosures herein relate to a substrate processing apparatus that supplies process gases to the surface of a substrate placed on a rotating rotary table in a vacuum chamber for the purpose of vacuum processing.
2. Description of the Related Art
A mini-batch-type vacuum processing apparatus is a device used in semiconductor processes for performing vacuum processing such as deposition and etching with respect to a substrate such as a semiconductor wafer (hereinafter simply referred to as a “wafer”). The mini-batch-type vacuum processing apparatus may include a rotary table for carrying wafers along a circumferential direction of a vacuum container and a plurality of process gas supply units situated above the rotary table. Vacuum processing is performed while rotating the rotary table that carries a plurality of wafers. This type of apparatus is suitable for the ALD (Atomic Layer Deposition) or MLD (Molecular Layer Deposition), which supplies a first reactant gas and a second reactant gas alternately to a wafer to deposit layers of atoms or molecules one over another.
Patent Documents 1 through 4 disclose examples of such apparatuses. In these disclosed apparatuses, the process area is sectioned such that reactant gases are not mixed on the wafer. A plurality of wafers are placed on a rotary circular table, which is rotated to revolve the wafers for processing. The use of such a mini-batch-type apparatus, however, may involve the following problems regarding the placement of wafers.
In the case of deposition by the ALD, a plurality of reactant-gas supply areas are provided within a chamber, and different reactant gases are supplied one after another to the wafers on a rotating rotary table. The gas supply areas into which the space in the chamber is divided have different gas flow amounts. When a wafer enters a low-pressure area from a high-pressure area, there is a risk of having the wafer blown off the table due to a high-pressure gas having intruded into a space behind the back face of the wafer during its passage through the high-pressure area.
In consideration of this, study has been underway to improve adhesion between the table surface and the wafer by adjusting the surface roughness of the wafer placement surface of the table. When a wafer is removed from or placed onto the table, a mechanism to lift up or down a wafer with respect to the table through elevation pins may be used. If the wafer placement surface is made into a mirror surface for the purpose of improving adhesion between the placement surface and the wafer, adhesion may become too strong, so that the wafer may be broken when it is lifted up by elevation pins. It is thus preferable to provide a proper degree of surface roughness for the wafer placement surface in order to ensure smooth wafer loading and unloading while improving adhesion between the placement surface and the wafer.
A strong centrifugal force is applied when the table rotates at high speed. A wafer may move from its originally loaded position due to this force despite the improved adhesion. As a result, the wafer placement surface may be scraped through friction between the surface and the wafer. Further, cleaning is performed at proper timing in deposition processes. The purpose of this cleaning is to remove extraneous substances from the vacuum container, so that a strong corrosive gas such as a gas containing fluorine is often used as a cleaning gas. As the number of cleanings increases, thus, the placement surface may be damaged. Upon providing optimum surface roughness for the placement table, therefore, the surface roughness may deviate from an acceptable range due to the above-described factors as a number of processes are performed.
In the ALD, a purge gas may be supplied into the vacuum container to purge the space below the placement table for the purpose of preventing the mixing of reactant gases with each other. Holes for inserting elevation pins for the purpose of loading and unloading a wafer may be formed through the placement table. With such holes, however, the wafer may be lifted when the flow amount of the purge gas is large. This may give rise to the problem that the flow amount of the purge gas cannot be set to a sufficient amount. This problem is not only observed in the ALD, but also observed in the CVD when the space under the placement table is purged for the purpose of preventing the intrusion of gases into the space under the table.    [Patent Document 1] Japanese Patent No. 3144664    [Patent Document 2] U.S. Pat. No. 7,153,542    [Patent Document 3] U.S. Patent Application Publication No. 2006-177579    [Patent Document 4] U.S. Pat. No. 6,869,641